This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/EP00/02209 which has an International filing date of Mar. 13, 2000, which designated the United States of America, the entire contents of which are hereby incorporated by reference.
The invention relates to a gas turbine rotor with an internally cooled gas turbine blade which has a blade foot and a blade platform, and with a disk possessing transverse disk grooves, into which the blade root is inserted. The blade platform is arranged outside an outer circumference of the disk and possesses, on an end wall portion of one longitudinal side, a recess into which is inserted an insert strip which engages into a corresponding recess of blade platform of a second gas turbine blade and bridges and seals off an interspace between the two blade platforms.
DE-A1-198 10 567 discloses a sealing plate for a gas turbine moving blade. When cooling air supplied to the gas turbine moving blade escapes into the high-temperature fuel-gas duct, this results, inter alia, in a reduction in the power output of the gas turbine. The sealing plate, which is inserted into the gas turbine blade, is intended to prevent cooling air from emerging. Sealing is carried out not only by way of the sealing plate, but also by way of various sealing pins which are installed between the platforms of two moving blades. A multiplicity of sealing elements is necessary in order to produce the desired function of sealing against the emergence of cooling air.
DE-B-1 258 662 discloses a covering device for guiding the cooling gas from gas turbine disks, which consists of a plurality of individual segments sealed off relative to one another by means of sealing strips. Sealing-off is therefore carried out in an additional device which is placed in front of the gas turbine disk and the gas turbine moving blades pushed into the latter. This increases the number of elements required for constructing the seal.
U.S. Pat. No. 4,523,890 discloses sealing elements for the root regions of turbine blades. Sealing serves for reducing the cooling-air losses at the lower end of the roots. To hold the sealing elements, it is necessary to introduce into the turbine disk holding grooves into which the sealing elements are to be pushed. Complicated production steps are therefore necessary.
Similar arrangements of sealing elements are also used to prevent the ingress of hot gas into the platform region or the internal cooling system of a gas turbine moving blade. Such an ingress of hot gas may lead to severe damage to the gas turbine moving blade. In order to prevent this, a plurality of sealing elements are inserted into the blade platform on that side of the blade platform of the gas turbine moving blade which faces the hot-gas stream.
Disadvantages of the built-on parts described for sealing the platform of the gas turbine moving blade prove to be that the seal is constructed from a multiplicity of elements and therefore it becomes difficult to install the seal in the gas turbine moving blade. In addition, various securing elements also have to be attached, in order to prevent the gas turbine moving blade from slipping out of place laterally in the rotating disk of the gas turbine or even falling out.
The object of the invention is to specify a gas turbine rotor with an internally cooled gas turbine blade, in which both sealing against the ingress of hot gas and the emergence of cooling air and the securing of the gas turbine blade are to be effected at a low outlay and at the same time are highly reliable.
The object is achieved in that the recess reaches as far as a disk-side base of the blade platform, and the insert strip has a form fit to the disk which secures against axial displacement in the direction of insertion of the gas turbine blade.
The specific design of the insert strip, in particular the extension of the latter as far as the blade platform, ensure, on the one hand, that the blade platform is sealed off at its end wall portion against the penetration of hot gas or the outflow of cooling air. Sealing can be produced in a simple way and is performed by a single element which can be individually adapted in its shape to various platform configurations.
At the same time, the insert strip ensures that the gas turbine blade is fixed axially in the disk of the gas turbine rotor. The gas turbine blade, which is inserted with its blade root into a transverse disk groove of the disk and the platform of which is arranged outside the circumference of the disk, therefore cannot be displaced relative to the transverse disk groove to an undesirable extent. Axial fixing is ensured by the form fit of the insert strip to the disk. As a result, in particular, the gas turbine blade is prevented from slipping out of place in the direction of insertion in which the forces acting during the running of the gas turbine may be preferentially directed. This type of fixing can be installed and removed in a particularly stable and simple way and has low susceptibility to faults.
After thermal expansion which occurs due to the load exerted by the hot gases flowing onto the wing, the insert strip returns completely into its neutral position, for example without being continuously displaced in relation to this, which, after a few runs of the gas turbine rotor, would lead to a failure of the functions of the securing element against displacement in a direction of insertion of the gas turbine blade in the transverse disk groove.
The sealing and fixing of the gas turbine blade are accordingly carried out by way of a single element, the insert strip. This constitutes an appreciable improvement, as compared with known systems, in which a multiplicity of elements and, in conjunction with this, a high outlay in terms of installation were necessary for this purpose. Another advantage, in addition to the simplicity with which securing is carried out by means of a single insert strip, is its good handleability and the possibility of quickly exchanging, cleaning or repairing it.
Preferably, highly heat-resistant material which is stable with respect to chemical attacks is to be used, so that the onflowing hot gas does not deform or corrosively destroy the insert strip. The proposed designs of the insert strip can easily be produced with these materials because of its simple shape and have high durability even where relatively brittle materials are concerned.
Comprehensive protection against axial displacements in both directions of insertion of the transverse disk groove is afforded in that there is a recess on each of the end wall portions of one longitudinal side of the blade platform, and in that its insert strips bear on two mutually opposite disk end faces and protect against axial displacements of the gas turbine blade relative to the disk. Securing against axial displacement or against a forward and backward slipping of the gas turbine blade inserted into the transverse disk groove is ensured by the two mutually opposite insert strips which in each case have a securing form fit on the two mutually opposite disk end faces of the disk. Axial movement is inhibited in as much as axial displacements of the gas turbine blade relative to the disk either are inhibited completely or are possible only within a predetermined small scope.
If there is a recess on each of the end wall portions of each longitudinal side of the blade platform and insert strips are inserted into said recesses, each gas turbine blade is secured by four insert strips, two strips in each case ensuring securing in one direction of insertion. In this way, even if one insert strip fails or is lost, the gas turbine blade is held securely against displacement in the transverse disk groove by the remaining three. In this case, in each case two gas turbine blades share between them the two insert strips seated between them in the longitudinal side of the blade platform.
The insert strips can be mounted with little outlay and are held particularly securely in the recess in that the recess runs obliquely in the direction of a longitudinal rotor axis of the gas turbine rotor and at its disk-side end issues into a chamfer of the disk head, said chamfer being oblique corresponding to the recess. By virtue of the oblique position of the inserted insert strips, the hot gases are deflected in the direction of the gas turbine wing and are therefore utilized optimally, without being swirled excessively by the blade platform or the blade platform being subjected to an excessively high thermal load. By the insert strip projecting beyond the blade platform and coming to bear sealingly on the oblique chamfer, good sealing-off against the penetration of hot gases into the blade platform or the emergence of cooling air is ensured.
The matched slopes provide uniform one-sided bearing contact of the insert strip on the recess of the chamfer of the disk head, with the result that acting forces, for example shear forces, which occur due to a relative displacement of the gas turbine blade in relation to another gas turbine blade or of the gas turbine blade in relation to the transverse disk groove, can be reliably absorbed, without the insert strip being subjected to excessive point load.
Simple securing against loss of the insert strip, for example because of acting centrifugal forces, is afforded in that the recess is open on the disk side and, with the gas turbine blade inserted in the transverse disk groove, the insert strip can be pushed into the recess on the disk side. In this case, after being pushed in, the insert strip is held, for example, by the closed wing-side end of the recess or in that it is designed to be widened at its disk-side end and engages behind an undercut of the recess, so that a form fit counter to the acting centrifugal forces is obtained.
Forces acting on the insert strip can be absorbed effectively, without the insert strip being destroyed, in that between the disk-side end of the recess and the outer circumference of the disk there is a gap allowing relative movements between the disk and the blade platform. Acting forces are, for example, shear forces which occur due to relative movements between the disk and the blade platform or due to the gas turbine blades being displaced relative to one another in the transverse disk grooves. The dimensions of the gap at the lower end of the recess are designed in such a way that the different acting forces can be absorbed by means of corresponding elastic deformations of the attached insert strip, so that a kind of xe2x80x9cspringback effectxe2x80x9d is achieved. Movements at the end of the insert strip are possible in the direction of insertion of the gas turbine blade and perpendicularly to this, depending on which of the acting forces have to be absorbed to a particularly great extent. If the axially displacing forces, in particular shear forces, are particularly high, it is expedient to select a gap with a very small height, so that the insert strip possesses sufficient rigidity to be capable of reliably accomplishing the axial securing.
The insert strip consists preferably of a material which possesses sufficient elastic deformation properties.
This is afforded, for example, by a highly heat-resistant alloy, such as nickel-based alloys. This makes it possible, at the same time, for the material of the insert strip to be selected in order to avoid impurities or diffusion damage and to ensure a uniform thermal expansion of the blade platform and the insert strip adapted to the material of the gas turbine blade.
A comprehensive hold of the insert strip is afforded by the recess being designed as a groove. The groove is preferably characterized by at least three walls which surround it and which form a form fit against the insert strip slipping out of place. Furthermore, the groove surrounding the sealing strip provides better sealing-off against onflowing hot gas or outflowing cooling air. The groove may be designed in such a way that it is laid sealingly around the insert strip and therefore seals off without additional sealing materials. In another embodiment, knife edges are attached to the groove and engage into the insert strip.
The groove provides, furthermore, increased safety against the actions of forces on the insert strip, for example shear forces, occurring due to relative displacements, of the platforms in relation to one another or of the platforms in relation to the disk. The groove is in this case opened on the side which is nearest to the adjacent platform. The insert strip can thereby easily be pushed into the two mutually opposite grooves and is seated there very securely.
An insert strip can easily be prevented from slipping through under the action of centrifugal forces by the recess being wider at its disk-side end than on its remaining part. A form fit is thereby made against the insert strip slipping through, and the latter can be inserted from the disk-side end of the recess, without the groove at the same time having to be closed at the upper end.
A secure hold of the insert strip when the gas turbine is at a standstill is obtained in that the insert strip is fixed in its push-in position on the disk. The insert strip is thereby prevented from slipping out of the recess even at a standstill when it is not pressed outward by the centrifugal-force load as a result of the rotational movement. Furthermore, fixing to the disk affords an improved hold against slipping out of place axially. Fixing may be carried out, for example, by means of a screw or a bolt which is presented below the insert strip and does not have to engage into the latter. This particularly simple type of fixing can be effected quickly and can also be canceled again quickly, even when corrosion has occurred.
To ensure that slip-through resistance is secured against loosening under the action of the centrifugal-force load, it is advantageous that there serves for fixing the insert strip a screw part which engages into a recess of the insert strip and is supported on the insert strip under the action of centrifugal force. By engaging into the recess of the insert strip, the screw part secures the insert strip against slipping out when the gas turbine is at a standstill. At the same time, since the screw part is supported on the insert strip under the action of centrifugal force, the insert strip prevents the screw part from slipping out. The two elements accordingly secure one another. This reduces the number of elements required. At the same time, the insert strip, in turn, can easily be removed, for example when gas turbine blades are to be exchanged.
The screw part can be supported on the insert strip in that the screw part has a projection which, when the gas turbine is at a standstill, bears directly on that surface of the insert strip which faces the disk, another part of the screw part reaching through the recess of the insert strip. In this case, it is necessary to ensure that that part of the screw part which is supported on the insert strip does not reach into emptiness as a result of the usual displacements occurring when the insert strip is under thermal load. This may be ensured in a simple way by the projection of the screw part coming to bear on the disk-side side of the insert strip all around the recess of the insert strip.
Securing the insert strip against falling out and/or securing the insert strip against being thrown out under the action of the centrifugal force, no additional parts being required, is accomplished in that the insert strip engages at a disk-side end into a securing recess of the disk end face. For engagement into this securing recess, the insert strip may, for example, already possess a bent-round end before insertion or be bent round after insertion into the securing recess. A further possibility is for the insert strip to possess an attached projection which, in the push-in position, matches the securing recess.
By virtue of such engagements into a securing recess in the disk end face, the insert strip can easily be removed for possible maintenance purposes or in the event of a failure of the gas turbine blade without additional tools or without the risk of the securing element caking together with the material under diffusive or corrosive attack at high operating temperatures. On the other hand, that part of the insert strip which engages into the securing recess may be designed with virtually any desired dimensions, so that securing is reliably afforded even in the event of high external forces. Furthermore, some play of the insert strip which engages into the securing recess is possible, so that thermal expansions or acting shear forces can be absorbed more easily without failure or damage to the insert strip.
Securing which is independent of the disk can be provided in that a securing strip leads through two insert strips below the blade platform and is bent round at its ends. Securing against slipping through is thereby afforded independently of the disk. This is advantageous when high shear forces occur which subject an insert strip fastened to the disk to high load and would possibly loosen it. This additional safety aspect is important particularly in the case of high temperature fluctuations or sharply alternating acting forces.
A good lateral hold and sealing-off of the insert strip is afforded in that the insert strip engages with a predetermined engagement depth into the recess of the blade platform, and in that the engagement depth of the insert strip into the recess is greater than the interspace between two adjacent blade platforms. Even under pronounced relative displacements of the blade platforms in relation to one another, the insert strip is held captive in the two recesses and seals off effectively here in a labyrinth-like manner.